Creating a Particle System: Animation Principles, Artifacts, and Extra Credit Ideas!

1. Particle systems • Good animation principles • Creating your artifact • Some extra credit ideas !

2. Agenda • Particle System - Requirements - What should I implement? - Suggestions - Cool forces

3. Agenda • Animating well vs. well… just animating • Timing! • Music • Light • Lasseter’s animation principles • Creating your artifact • Selecting a curve type • Compositing

4. Particle System requirements • Particle System class • Should have pointers to all particles and a marching variable (time) for simulation • If you have two separate simulations (say, cloth sim and particles that respond to viscous drag) you may want to make that distinction here (as well as in your force and particle implementation) • Solver • In the skeleton, this actually exists within the Particle System class • Particles

5. Particle System requirements • At least one force • Collision detection • With one primitive of your choice • Restitution coefficient must be slider controlled

6. Particle SystemWhat should I implement? • Canonical components • Constructor • Destructor • etc • Simulation functions • drawParticles() • startSimulation() • computeForcesAndUpdateParticles() • stopSimulation()

7. Particle SystemWhat should I implement? • Particle struct or class • you may have several of these if you have multiple types of simulations • If this is the case, take advantage of inheritance • Force class • An elegant implementation would include a generic Force class and a variety of distinct forces that inherit from it *Note: I stress inheritance because it will make your implementation easier (and less messy) and in general will make your life easier. If the TA that grades your project must look at your code, clean object oriented code is a great headache-prevention-tool.

8. Particle SystemEmbedding in your hierarchy • Need to find World Coordinates of Particles - Model View Matrix - Inverse Camera Transformation - Generate world coordinate for particles by undoing camera transformations to the point you want to launch from. • Euler Method • Hooking up your particle System

9. Particle SystemCool Forces • Particles in a lattice • Cloth simulation • Deformable objects • Flocking • Will require multiple forces: • Attractive force that affects far away particles • Repulsive force that affects nearby particles • What else?

10. Animating well vs. well… just animating • Timing! • Timing is VERY, VERY important • Consider timing before you bother to get specific about joint rotations or object positions

11. Animating well vs. well… just animating Good timing

12. Animating well • Music! • Sound and music can greatly enhance the cohesion of your artifact • If your artifact idea includes a theme or stylization, it can be very effective to time your animation with events in the theme music. Good sound

13. Animating well • Light! • Like sound, light is VERY VERY important compositionally • Anything you can do to be creative with lighting will help Light vs. No light

14. Creating Your Artifact • Choice of curve types • Catmull-Rom is usually the preferred curve choice… • but unless your project supports the option to add C1 discontinuity at will, you might find yourself trying to fight the Catmull-Rom to create pauses and other timing goodies

15. Creating Your Artifact • Compositing • Recommended that you break your intended artifact up into shorter clips combining them all in the end. • This will make your life easier for many reasons: • Splitting up work is straightforward • Changing camera angles is GOOD for a composition • You can incrementally complete your artifact • Adobe Premiere • Play around with it, check the website for some details on how to use it. The user interface is pretty intuitive.

16. Extra Credit ideas • Tension control for Catmull-Rom • Interpolating splines are cool because keyframing the parameter values that you want is more intuitive… • But what about the time instances not keyed? Without control of curve tension, you may not get the parameter values that you would really like, and your animation could suffer • Allow control points to have C0, C1, or C2 continuity • This can be VERYhelpful in creating a good animation • Initialize particle velocity with velocity of model hierarchy node to which it is attached • This is fairly easy and will make your particle system noticeably more realistic

17. Extra Credit ideas • Billboarding • Adding support for sprites (billboarding) can DRASTICALLY increase the aesthetic quality of your simulation • Additional benefit: very easy to ‘skin’ particles and make multiple instance of same particle look unique • Baking • A must for complicated simulations or for particle systems with a lot of particles

18. Extra Credit ideas • Better collision detection • Better forces • Lens flare • Most animator artifacts suffer from lack of realistic looking lighting • Ideally, this problem would be solved with ray tracing or photon mapping • Since these are probably not options, lens flare is an alternative way to give the impression of interesting lighting

19. Any Questions? Email the staff! csep557-staff@cs.washington.edu